Conventional offset printing presses typically comprise a rotationally supported plate cylinder, a blanket cylinder and an impression cylinder. Ink or emulsion ink is supplied to the image area of the plate cylinder(s), from where it is transferred to the blanket cylinder and ultimately to the paper or paper web running between the blanket cylinder and the impression cylinder. As is known, by placing blanket cylinders on both sides of the paper, images may be applied to both sides of the paper simultaneously, often referred to as perfect printing.
Typically, the cylinders are formed by turning the ends of solid metal cylinders to form journals, with the journals at each end including bearings which, in turn, are mounted in support frames on each end of the cylinders. Also, typically, each blanket cylinder is wrapped with a flexible blanket sheet having a pair of ends. The sheet is stretched around the cylinder such that the ends meet. The ends are then tucked into special retaining slits cut along the length of the blanket cylinder. The discontinuities in the cylinder caused by these slits and/or the resulting gap between the ends of the sheet cause vibration of the cylinders and other press components. These vibrations have a tendency to negatively impact the printed image and limit the speed of the press.
A conventional plate cylinder is constructed much like the blanket cylinder, with the exception that, instead of a blanket covering, the cylinder is clad with an image carrying plate. In order to secure the image plate to the cylinder, the underlying cylinder includes a lock up gap.
Typically, once the size of the blanket cylinder(s) and the plate cylinder(s) are chosen, the size of the resulting image cannot be changed without changing many of the press components including, for example, the cylinders, the driving gears, aspects of the supporting frame, and other components.
Conventionally the image plate is inked by a series of rubber rollers alternating with metallic or polymer covered rollers which oscillate laterally to better distribute ink. These rollers are driven by the gears mounted on the end of the cylinders. The cylinders and the inking rollers are supported at each end by the press frame.